Method for controlling time point for data output in synchronous memory device

Abstract

Disclosed is a method for controlling a time point for data output in a synchronous memory device, which varies a time point of an internal read command of the synchronous memory device, which is generated in response to an external read command according to the CAS latency of the synchronous memory device. In other words, the time point to generate the internal read command when CAS latency corresponds to 2N+2 (N=0, 1, 2, . . . ) is delayed by 1tCK as compared with the time point to generate the internal read command when CAS latency corresponds to 2N+1, and the 1tCK is a period of an external clock applied to the synchronous memory device.

1. A method for controlling timing for data output of a synchronous memory device, the method comprising the step of:
 varying the timing of an internal read command of the synchronous memory device, which is generated in response to an external read command according to the CAS latency of the synchronous memory device, wherein the varying step is dependent on the CAS latency having an odd number or an even number, the varying step includes:
 delivering directly the internal read command of the synchronous memory device from an external device at a first time point when the internal read command corresponds to the CAS latency having an odd number defined by 2N+1 (where N=0, 1, 2, . . . ); and 
 delaying the internal read command of the synchronous memory device from the external device at a second time point when the internal read command corresponds to the CAS latency having an even number defined by 2N+2 in which the first and second time points are substantially identical when the delivering and delaying steps share a common N value. 
 
 
   
   
     2. The method as claimed in  claim 1 , wherein the second time point to generate the internal read command when CAS latency corresponds to 2N+2 (N=0, 1, 2, . . . ) is delayed by 1tCK as compared with the first time point to generate the internal read command when CAS latency corresponds to 2N+1, and the 1tCK is a period of an external clock applied to the synchronous memory device. 
   
   
     3. The method as claimed in  claim 2 , wherein a plurality of control signals are outputted in response to the internal read command, the control signals being used for controlling a plurality of timed points to enable a data output driver of the synchronous memory device. 
   
   
     4. The method as claimed in  claim 3 , wherein each of the control signals is generated with a time interval of 2tCK. 
   
   
     5. The method as claimed in  claim 4 , wherein one of the control signals is selected according to the CAS latency. 
   
   
     6. A method for controlling a data output timing of a synchronous memory device, the method comprising the steps of:
 delivering a first control signal to the synchronous memory device from an external device at a first time point when the first control signal corresponds to a CAS latency having an odd number defined by 2N+1 (where N=0, 1, 2, . . . ); and 
 delaying a second control signal to the synchronous memory device from the external device at a second time point when the second control signal corresponds to the CAS latency having an even number defined by 2N+2 in which the first and second time points are substantially identical when the delivering and delaying steps share a common N value, 
 wherein the first control signal controlling the data output timing when the CAS latency of the synchronous memory device corresponds to 2N+2 (N=0, 1, 2, . . . ), and the second control signal controlling the data output timing when the CAS latency corresponds to 2N+1. 
 
   
   
     7. The method as claimed in  claim 6 , wherein the first time point to generate a first internal read command by receiving an external read command when the CAS latency corresponds to 2N+2 is delayed by 1tCK as compared with the second time point to generate a second internal read command by receiving the external read command when the CAS latency corresponds to 2N+1, the first internal read command being used in the synchronous memory device, and the 1tCK is a period of an external clock applied to the synchronous memory device. 
   
   
     8. The method as claimed in  claim 6 , wherein the data output timing when the first control signal is generated from after the first internal read command is generated is identical to the data output timing when the second control signal is generated from after the second internal read command is generated. 
   
   
     9. A method for controlling timing for data output of a synchronous memory device, the method comprising the steps of:
 generating an internal read command varying with the CAS latency having an odd number or an even number; 
 generating the first internal counter signal which is a control signal used for controlling a time point for read data output by receiving the internal read command; 
 generating a number of the second internal counter signal in synchronization with a rising edge of a DLL clock; and 
 generating a number of the third internal counter signal in synchronization with a falling edge of the DLL clock using one of the second internal counter signals.